[GHC] #10735: Smooth out the differences between `compiler/utils/Pretty.hs` and `libraries/pretty`

[GHC]

#10735: Smooth out the differences between `compiler/utils/Pretty.hs` and
`libraries/pretty`
-------------------------------------+-------------------------------------
        Reporter:  thomie            |                   Owner:  thomie
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.0.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #1062, #1176,     |  Differential Revisions:  Phab:D1130
  #7666, #8809                       |
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Comment (by Thomas Miedema <thomasmiedema@…>):

 In [changeset:"6f6d082124b24bd8437f95d99a8fd8844a0f6cd8/ghc" 6f6d082/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6f6d082124b24bd8437f95d99a8fd8844a0f6cd8"
 Pretty: Args of NilAbove/TextBeside/Nest/Union are always RDocs (#10735)

 Just following libraries/pretty.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10735#comment:10>
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